1. Field of the Invention
The present invention relates to a stored data protection apparatus for an electronic device such as electronic notebook, pocket computer and the like, having a volatile memory which maintains stored data by a battery power supply.
2. Description of the Related Art
In general, an electronic device having a computer, for example such as an electronic notebook, a pocket computer and the like carries a main battery for normally supplying power to both of a CPU (Central Processing Unit) and a RAM (Random Access Memory) in the device, and a back-up battery for supplying power to the RAM when the power supply voltage from the main battery is reduced or such main battery is taken out from the device for replacement, so as to prevent data stored in the RAM or other volatile memory from being destroyed.
In case that the main battery is replaced with a new one with the assistance of the back-up battery, a singing phenomenon often occurs in power supply voltage. More particularly, the singing phenomenon is most likely to occur when a new main battery is set in the electronic device. Such singing phenomenon may cause the CPU of the device to erroneously respond to its instructions, so that there is a fear that a wrong data is written into the RAM to destroy the data having been already stored in the RAM.
In order to solve the above problem inherent in the conventional electronic device, the device is generally provided with a manually operated switch For blocking off a chip-enable signal issued from the CPU to the RAM, and a manually operated reset switch for resetting the CPU. For replacing the main battery with a new one, a user of the device has to sequentially operate these manual switches in a predetermined order.
Replacement of the main battery with a new one is performed as follows. First of all, after the device is put in a stand-by mode, the manual switch is turned off so as to block off the chip-enable signal. Then, the old main battery is replaced with a new one. After that, the reset switch is manually operated so as to reset the CPU. Finally, the manual switch is turned on to permit the chip-enable signal to be applied to the RAM. Through the above sequential manual operation conducted by the user, it is possible to prevent the stored data from being destroyed even if the CPU runs away during the replacement of the main battery.
However, since it is necessary for the user to manually operate the switches sequentially, there is a fear that the user will make some mistakes in the above manual operation to cause the stored data to be destroyed. Furthermore, even when the above manual operation is properly conducted by the user, there is still a fear that the CPU runs away to cause the stored data to be destroyed when the new main battery now set in the device can not supply, to the RAM, sufficient power necessary for maintaining the stored data in the RAM.